How it works
A physical change is a change in the shape, size, or state of matter, but the substance itself stays the same. No new substances are made. Examples include cutting paper, melting ice, or crushing a can.
A chemical change is when a substance changes into something new. This often happens with heat, color change, gas production, or making a new substance. Examples include burning wood, rusting iron, or baking a cake.
How to tell the difference:
- If you can get the original material back easily, it's usually a physical change.
- If a new substance is made and you can't easily change it back, it's a chemical change.
Key words to look for:
- Physical change: melt, freeze, break, cut, crush, dissolve
- Chemical change: burn, rust, rot, react, cook, decompose
Worked example
Which change is physical rather than chemical? A) Water boils on the stove. B) Bread turns brown when toasted. C) A nail rusts in the rain. D) Milk sours.
- 1
Look at each choice and decide if a new substance is made.
Physical changes do not make new substances; chemical changes do.
- 2
A) Water boils on the stove.
Boiling is just water changing from liquid to gas—still water. It's a physical change.
- 3
B) Bread turns brown when toasted.
The bread is changing into new substances (it can't be 'untoasted'). This is a chemical change.
- 4
C) A nail rusts in the rain.
Rust is a new substance made from iron and oxygen. This is a chemical change.
- 5
D) Milk sours.
Sour milk is chemically different from fresh milk. This is a chemical change.
Answer
A) Water boils on the stove. (Physical change)
Common mistakes
- 01
Thinking any change in appearance is chemical.
Why: Students see something looks different and think it must be new.
Avoid it: Ask: Can I get the original material back? If yes, it's physical.
- 02
Confusing breaking or crushing with chemical changes.
Why: Breaking things seems dramatic, but the substance is still the same.
Avoid it: Remember: Only the size or shape changed, not what it's made of.
- 03
Missing clues like 'burns' or 'rusts' indicating chemical change.
Why: Students may not know these are chemical processes.
Avoid it: Learn key words that signal a chemical change: burn, rust, react, cook.
Practice
Answers stay hidden
1.Which of the following is a physical change? A) Burning a candle B) Melting butter C) Baking a cake D) Cooking an egg
Show hint
Does the substance stay the same after the change?
Reveal answer
B) Melting butter
2.Which is a chemical change? A) Breaking a pencil B) Dissolving sugar in water C) Silver tarnishing D) Chopping carrots
Show hint
Look for a new substance being made.
Reveal answer
C) Silver tarnishing
3.Which is a physical change? A) Leaves turning brown in the fall B) Ice cream melting C) Wood rotting D) Bread rising when baked
Show hint
Think about whether you can get the original substance back.
Reveal answer
B) Ice cream melting